🐛(react) disable button link

According to its prop, the Button component can be rendered as
a link but in this case, the prop `disabled` has no effect. So to fix
that if the Button receives a `href` prop and is disabled, we apply
a modifier class `.c__button--disabled`.

packages/react/src/components/Button/_index.scss

@@ -32,7 +32,7 @@
     border-color: currentColor;
   }
 
-  &:disabled {
+  &:disabled, &.c__button--disabled {
     background-color: var(--c--theme--colors--greyscale-200);
     color: var(--c--theme--colors--greyscale-600);
     cursor: not-allowed;